The regulation of purine nucleotide biosynthesis and the interconversion of purine 5'-monophosphates are being studied. Specific enzymes under investigation include adenylosuccinate synthesis, adenylosuccinate lyase and AMP aminohydrolase. Relationships between different isozymes are being evaluated to understand the regulation of the system in normal and neoplastic cells. Also antimetabolites such as alanosine and 6-mercaptopurine are being studied to determine their mode of action. Additional studies under this project include kinetic investigations of gamma-glutamylcystine synthetase, pyruvate carboxylase, glutamine synthetase and aspartase.